1. Field of the Invention
The present invention relates to an optical pickup installed in an optical disk drive and, in particular, to an optical pickup including an actuator in which a movable side lens holder provided with an objective lens is supported in a displaceable manner in a cantilever state by elastic wires extending from a fixed side support member.
2. Description of the Related Art
An optical pickup installed in an optical disk drive is used for focusing laser light on a disk surface serving as a recording medium and thereby for writing and reading data. Such an optical pickup has the function of adjusting the position of the objective lens in the focusing direction or the tracking direction in response to surface deflection and off-centering during the rotation of the disk.
FIG. 4 schematically shows an actuator 1 adopted in a prior art optical pickup. The actuator 1 of the figure is mounted on a base (not shown) driven and thereby traveling in a radial direction of a disk. The actuator 1 includes: a fixed side support member 2 fixed to the base; a movable side lens holder 3 provided with an objective lens 31; a wiring board 4 adhered to the rear end face of the fixed side support member 2; terminal plates 5 and 5 each composed of a wiring board adhered to each of both side faces located in the right and the left direction of the movable side lens holder 3; and electrically conductive wires 6 . . . having elasticity and arranged in the same number on each of the right and left sides of the actuator 1. Further, the movable side lens holder 3 is provided with a plurality of coils (not shown) for generating a biasing force in a focusing direction For a tracking direction T. The end portions of these coils are connected to patterns of the terminal plates 5. A plurality of these wires 6 . . . and these terminal plates 5 are arranged symmetrically on both right and left sides of the actuator 1. In the example of the figure, three wires 6 are arranged on one side. However, although not shown, two wires 6 can be arranged on one side in some cases. Then, one-end portions 61 of the wires 6 are soldered and fixed to lands of the wiring board 4, while the other end portions 62 are soldered and fixed to lands of the terminal plates 5 so that the movable side lens holder 3 is supported in a displaceable manner in the form of a cantilever by the fixed side support member 2 via a plurality of the wires 6 . . . . Numerals 41 and 51 indicate solder. Spaces 7 each having the same volume are arranged in a plurality of sites of each side face located in the right and the left direction of the fixed side support member 2. Three spaces 7 are stacked vertically in three decks each corresponding to each individual wire 6 so that each wire 6 is inserted through the inside of a layer of a damper material (not shown in FIG. 4) filling each individual space 7.
In the actuator 1 of FIG. 4, when an electric current is supplied to the pattern of the wiring board 4, the above-mentioned coils are energized through the wiring board 4, the wires 6, and the terminal plates 5 so that the coils generate a biasing force in the focusing direction or the tracking direction. As a result, the movable side lens holder 5 is driven and displaces in the focusing direction For the tracking direction T together with the objective lens 31.
FIG. 5 is an enlarged horizontal sectional plan view showing the main part of the fixed side support member 2. In the figure, numeral 8 indicates a damper material filling the space 7 (see FIG. 4). The above-mentioned wire 6 is inserted through the inside of the layer of this damper material 8. This damper material 8 is composed of a gel substance of a photo-curing type, thermosetting type, or the like, and provides the effect of suppressing the primary resonance of the wires 6 occurring when the movable side lens holder 3 is driven and displaces by means of the deflection deformation of the wires 6.
Each space 7 provided independently in correspondence to each wire 6 shown in FIG. 4 is composed of a groove shaped cavity surrounded by a groove shaped surface 71 formed in a C shape or an approximate C shape viewed from the front. The entirety of the groove shaped cavities (that is, the spaces 7) is open in the front surface, the rear surface, and a side face of the fixed side support member 2.
Meanwhile, in an optical system supporting apparatus in which a retention member for supporting an optical element such as an objective lens is supported by a support spring having a leaf spring shape, a prior art technique is known that a damping gel material is applied to a retention section provided integrally near an end portion of the support spring so that the control characteristics of the optical system supporting apparatus are stabilized (see Patent Document 1, for example). Further, in an optical system supporting apparatus, a prior art technique has been proposed that an end of an elastic metal member for supporting a lens holder is fixed to a first space region provided in a fixed member with adhesive, and that an elastic gel material is then caused to fill a second space region adjacent to the first space region so that the elastic gel material is prevented from overflowing from the second space region (see JP-A-2002-352451 for example).
As described above, in the prior art example described with reference to FIG. 4, each space 7 for holding the damper material 8 is composed of a groove shaped cavity surrounded by the groove shaped surface 71, while the entirety of the spaces 7 is open in the front surface, the rear surface, and a side face of the fixed side support member 2. Thus, when each space 7 is charged with a fixed amount of the damper material 8 by using these open portions, the surface shape of the damper gel material 8 exposed in each of these open portions of the spaces 7 hardly becomes uniform, so that the situation could have occurred whereby the surface shape of the damper material 8 varies depending on each of the open portions of the spaces 7. For example, the surface shape of the damper material 8 is different among the open portions of the spaces 7 located on one of the right and left sides of the fixed side support member 2. Alternatively, the surface shape of the damper material 8 of the open portions of the space 7 located on one of the right and left sides of the fixed side support member 2 are different from that of the other side.
Further, when such a difference in the surface shape of the damper material 8 occurs in the open portions on the front surface side of the spaces 7, this causes a difference among the wires 6 with respect to the wire length (effective length of the wire) measured between the front surface of the damper material 8 through which the wire 6 is inserted and the portion soldered with the terminal plate 5 in the other end portion 62 of the wire 6 shown in FIG. 4. This causes a difference in the spring constant of each wire 6 imparted to the actuator 1, and hence causes a variation in the primary resonance frequency of the wires 6 or in the so-called DC sensitivity. This causes difficulty in achieving stability in the characteristics required in the actuator 1.
FIG. 5 shows an example of the surface shape of the damper gel material 8 filling a space 7 of the fixed side support member 2 of the prior art actuator 1 described in FIG. 4. In this example, the front surface 81 of the damper gel material 8 in the front surface side open portion 700 of the space 7 has such a curved shape that the surface is located more backward with increasing distance from the rear wall (groove bottom surface) of the groove shaped surface 71. In this case, if the surface of the front surface 81 of the damper gel material 8 is in the same curved shape among the front surface side open portions 700 of the spaces 7, the effective length of the wire 6 becomes the same among the wires 6, and hence almost no variation occurs in the primary resonance frequency of the wires 6 or in the so-called DC sensitivity. In contrast, if the surface of the front surface 81 of the damper gel material 8 filling the space 7 is individually in a different curved shape, the position of the crossing portion of the front surface 81 of the damper material 8 with each wire 6 inserted through the damper material 8 becomes different depending on the wire 6. Thus, the effective length of each wire 6 varies depending on the wire 6, and hence the spring constant of each wire 6 becomes different. This causes a variation in the primary resonance frequency of the wires 6 or in the so-called DC sensitivity, and hence causes instability in the characteristics of the actuator 1. This can degrade the stability in the read and write performance of the optical pickup.
In this point, the technique described in JP-A-6-314432 is merely that the retention portion for the damping gel material is provided in the support spring itself. Thus, this technique is hardly applicable to the prior art example of the actuator 1 described in FIG. 4 where the damper material 8 is caused to fill the space 7 provided in the fixed side support member 2. Even if applicable, the technique cannot avoid the variation in the surface shape of the front surface 81 of the damper material 8.
On the other hand, the technique described in JP-A-2002-352451 is a procedure that an end of an elastic metal member is fixed to a first space region provided in a fixed member with adhesive, and that an elastic gel material is then caused to fill a second space region adjacent to the first space region. This causes the necessity of an extra step of applying the adhesive before the process of filling the elastic gel material, and hence increases complexity in the work.